The disclosure of Japanese Patent Application No. 000-234383, filed Aug. 2, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the invention
The invention relates to an endless metallic belt and a manufacturing method therefor. More particularly, the invention relates to reinforcement of a hoop of a CVT (Continuously Variable Transmission) belt or the like.
2. Description of the Related Art
An endless metallic belt is mounted on two rollers for traveling. When traveling on a roller, the belt is subjected to a tensile bending stress at its outer peripheral surface. When leaving the roller toward the next roller, the belt is straightened and is relieved of the tensile stress at the outer peripheral surface resulting from bending. During traveling, the outer peripheral surface of the belt is thus repeatedly subjected to the tensile stress by bending. It is therefore desired to improve fatigue strength of the belt against such repeated tensile stresses.
Japanese Patent Laid-Open Publication Nos. 61-42402 and 63-96258 propose an endless metallic belt with improved fatigue strength at its outer peripheral surface. More specifically, only the outer peripheral surface of the endless metallic belt is subjected to shot peening so as to produce a compressive residual stress at the outer peripheral surface, thereby improving the fatigue strength.
In an endless metallic belt formed from a thin plate, however, the ratio of the thickness of the layer of the induced residual stress to the plate thickness is of a considerable level. As shown in FIG. 8, a belt 6xe2x80x2 is significantly deformed i.e., deformed into multiple small hoops as a result of shot peening. Hereinafter, such deformation will be referred to as multi-hoop deformation. This is because the circumferential radius of curvature is reduced in every part of the belt due to the relief of the compressive residual stress applied to the shot-particle ejected side i.e., the outer peripheral surface of the belt. Accordingly, shot peening of certain intensity or more cannot be applied to the endless metallic belt formed from a thin plate i.e., shot peening can be conducted only to such a degree that does not cause multi-hoop deformation, hindering sufficient improvement in fatigue strength.
It is an aspect of the invention to provide an endless metallic belt having improved fatigue strength without suffering any significant deformation, and a manufacturing method therefor.
In order to achieve these aspects, an endless metallic belt is provided which has at its outer peripheral surface a layer provided with a compressive residual stress by shot peening, and also has at its inner peripheral surface a layer provided with a compressive residual stress by shot peening. This endless metallic belt is produced by a manufacturing method in which both outer and inner peripheral surfaces of the endless metallic belt are subjected to shot peening. For example, with the endless metallic belt being mounted on at least two rollers, the inner peripheral surface is shot peened during traveling of the endless metallic belt, and then the endless metallic belt is reversed and the outer peripheral surface is subsequently shot peened during traveling of the endless metallic belt.
In the aforementioned endless metallic belt and manufacturing method therefor, both inner and outer peripheral surfaces of the endless metallic belt are subjected to shot peening. Therefore, a layer of compressive residual stress is formed by the shot peening both at the inner and outer peripheral surfaces of the endless metallic belt. Thus, deformation of the belt resulting from relief of the compressive residual stress at the inner peripheral surface cancels deformation of the belt resulting from relief of the compressive residual stress at the outer peripheral surface, preventing significant deformation (multi-hoop deformation) of the endless metallic belt. As a result, high-level shot peening as well as a compressive residual stress produced thereby can be applied to the outer peripheral surface of the belt, whereby the fatigue strength at the outer peripheral surface of the belt can be improved over the conventional examples.